1. Field of the Invention
The invention relates to providing a cyclic dewaxing/regeneration operation for hydrocarbon feedstocks. In particular, it relates to a cyclic process which includes regenerating a catalyst comprising palladium and a zeolite having the structure of Zeolite Beta, which has been deactivated by coke buildup or poisoning. Catalysts which may be employed by the process of the present invention include those deactivated during hydrocarbon hydroprocessing, such as catalytic dewaxing by isomerization of hydrocarbon feedstocks.
2. Discussion of the Prior Art
Catalytic dewaxing of hydrocarbon feedstocks, such as distillate fuel oils and gas oils, by isomerization over a Zeolite Beta catalyst comprising a noble metal of Group VIIIA, such as platinum, palladium, etc. is known in the art. U.S. Pat. No. 4,419,220 to LePierre et al discloses such a process. However, the isomerization catalyst is deactivated by coke buildup or poisoned by materials, such as nitrogen, or heavy metals, such as vanadium. A detailed background on catalysis, catalyst poisons and catalyst regeneration and rejuvenation is provided by "Catalyst Deactivation and Regeneration", Chemical Engineering, Vol. 91, No. 23, pp. 96-111, Nov. 12, 1984. Rejuvenation generally characterizes reactivation processes employing halogen, whereas regeneration generally characterizes reactivation processes not employing halogen.
Isomerization employs a dual function catalyst and, for proper operation, a metal-to-acid (zeolite) balance must be maintained. The dual functions are metal for hydrogenation and zeolite for hydrocarbon isomerization/cracking. Studies on metal sintering on emorphous catalysts indicated palladium catalysts tended to sinter more than platinum catalysts. Continued developments found better techniques for applying palladium while reducing the tendency to sinter.
U.S. Pat. No. 4,232,181 to Kiovsky et al discloses a method of isomerizing pentane utilizing palladium-exchanged Mordenite.
Reactivation of platinum catalysts utilized in hydrocarbon hydroprocessing procedures, such as reforming, is known in the art. Processes which utilize chlorine and oxygen in catalyst reactivation are particularly well known. For example, U.S. Pat. No. 2,906,702 to Brennan et al discloses a method of restoring an alumina-supported platinum catalyst after deactivation caused by the reforming of hydrocarbons. This method teaches contacting a deactivated platinum-alumina catalyst with a gaseous chlorine, fluorine, or other halogen or halogen-affording substance at an elevated temperature.
U.S. Pat. No. 3,134,732 to Kearby et al teaches a method for reactivating a noble metal catalyst supported on alumina by contacting the catalyst with halogen-containing gas, stripping excess halogen therefrom, and subjecting the resulting catalyst to a reduction step with a hydrogen-containing gas. In this disclosure, the agglomerated metal is present on the surface of the alumina as small crystals.
It is also known in the art to reactivate noble metal and platinum group metal-containing zeolite catalysts. Reactivation of noble metal-loaded zeolite catalysts requires certain procedural modifications to regain the activity of the metal. U.S. Pat. No. 3,986,982 to Crowson et al treats deactivated platinum group metal-loaded zeolites by contacting them with a stream of an inert gas containing from 0.5 to 20% volume of free oxygen and from 5 to 500 ppm volume of chlorine as chlorine, HC1, or an organic chlorine-containing material. The resulting catalyst is purged to remove residual oxygen and chlorine, and then reduced in a stream of hydrogen at 200.degree. to 600.degree. C.
The treatment of noble metal-containing catalyst materials with sulfur compounds is also known in the art. For example, U.S. Pat. No. 3,661,768 to Davis, Jr. et al describes a method of reactivating a bimetallic reforming catalyst, such as platinum-rhenium, on alumina, which includes contacting the catalyst with hydrogen sulfide to convert platinum to platinum sulfide. Prior to sulfiding, the catalyst is contacted with chlorine and steam in order to effect chlorination.
U.S. Pat. Nos. 3,069,362 and 3,069,363 to R. L. Mays et al disclose coke removal by oxidative burn-off under controlled conditions of oxygen concentration, temperature and water vapor concentration. However, this method is not effective for dual function catalysts; that is, catalysts which contain an active metal, as noted above, because it deactivates the metal.
British Pat. No. 1,148,545 discloses a process that is effective for decoking a dual function catalyst, comprising heating the catalyst from oxidative burn-off at a temperature of at least 800.degree. F. (427.degree. C.), cooling the catalyst to below 600.degree. F. (316.degree. C.) and partially rehydrating the catalyst, and contacting the partially rehydrated catalyst with hydrogen at a temperature of at least 850.degree. F. (454.degree. C.). However, this involves the hydration and repeated heating and cooling steps, which may cause expansion and contraction of catalyst, and resulting catalyst attrition.
U.S. Pat. No. 4,358,395 to Haag et al discloses zeolite catalyst regeneration in which a zeolite catalyst is contacted with oxygen, then precoked under controlled conditions and then contacted with hydrogen (H.sub.2) gas under controlled conditions. This process has the drawback of requiring the precoking step.
Catalyst regeneration employing oxidation or reduction may be conducted either in situ within a reactor or offsite outside of the reactor. Offsite regeneration may comprise contacting a thin layer of catalyst on a moving belt with the oxidating or reducing gas. There are some benefits to offsite reduction because it allows high temperature throughout of oxygen without danger of temperature runaway. Also, impurities are removed from the catalyst layer without having to contact other catalyst downstream in the same layer, as is the case for in situ regeneration.
All of the above halogen treatment require certain precautions owing to the corrosive nature of the halogens used. In addition, certain halogen materials employed in these processes and significantly to the cost of catalyst reactivation. In order to avoid the drawbacks associated with halogen use, it would be advantageous to reactivate catalysts in the absence of halogens. However, when deactivating coke present on a catalyst material is exposed to an oxidizing atmosphere consisting of oxygen and an inert gas, such as nitrogen, substantially all of the noble metal present on the catalyst then becomes catalystically inactive.
It would be desirable to find a catalyst for catalytic dewaxing by hydroisomerization which can be regenerated by simple oxidation or combinations of oxidation and reduction. This would potentially eliminate or reduce the need for the use of troublesome and corrosive halogen rejuvenation procedures, or oxidation and reduction procedures which incorporate additives or additional steps, such as precoking. This would result in improving and simplifying the performance of cyclic dewaxing/regeneration processes and significantly increase processing time.